In the production of fluids such as oil, gas and water from inaccessible subsurface earth formations, it is conventional practice to drill a well penetrating the formation of interest, case the well and perforate the casing opposite the formation of interest and, in many cases, dispose a production tubing in the casing. Fluids are then produced through the casing performations and up the tubing or from an open hole below the casing by natural pressure forces, natural water drive or natural gas drive or a pump is mounted on the lower end of the tubing. To the extent that natural forces or pumping are inadequate, it is also common practice to inject displacing fluids into the well either periodically with periodic production cycles or into a separate injection well or wells penetrating the formation of interest.
In many cases the fluid-containing formation of interest comprises an unconsolidated sand. As a result, during production sand passes into the well and through the producing equipment along with produced fluids. Serious problems are created by such sand production, including, primarily, severe erosion of downhole equipment and plugging of the casing perforations, producing equipment or the entire bottom of the well. This problem is overcome in one of two conventional manners, namely, by gravel packing the bottom of the well opposite the formation of interest, simply by filling the bottom of the well with gravel, or by consolidating the unconsolidated sand formation immediately adjacent the well. It is also common practice and preferred to consolidate a gravel pack to form a solid, permeable pack. A particularly useful consolidating material is an epoxy resin. The epoxy resin may be deposited by introducing a fluent single composition of an epoxy compound, a curing agent for the epoxy compound, a solvent adapted to maintain the epoxy in a fluent condition until it is in place, a diluent and, optionally, a cure retarder. The solution is pumped down the well and into the sand surrounding the well or into the gravel pack or both, the fluid is maintained in place for a time sufficient to form an intermediate resinous reaction product between the curing agent and the epoxy compound, which precipitates from the solution onto the surface of the sand or gravel particles and which precipitate prefentially wets the sand or gravel particles by virtue of other components of the composition, such as certain curing agents. Further, contact time then converts the epoxy coating on the particles to a hard epoxy resin and, at the same time, cements the particles together. Excess treating solution containing the epoxy resin is then removed from the void spaces between the particles, by washing the same out with an appropriate external fluid or fluid produced from the formation, to thus produce a permeable consolidated mass of sand and/or gravel.
Another problem often encountered in the production of fluids from subsurface formations is the deposition of materials present in the produced fluids or produced along with the produced fluids, for example, waxes and asphalts contained in produced oils and inorganic solids. The buildup of such deposits obviously tends to plug the casing perforations and the producing equipment, thereby restricting flow of the fluids to be produced. One method of preventing the deposition and buildup of these materials is to deposit a coating of an epoxy resin on the surfaces of the casing, the tubing and well equipment which is in contact with the produced fluids. The epoxy coating, in this case, need not be completely cured to a hardened coating but may simply be a coating of the intermediate precipitated product which remains soft. However, in either case, the coating adheres to the well equipment and presents a smooth, slick surface which resists formation of deposits thereon. The epoxy resin coating may be deposited on the equipment in the same manner utilized in sand or gravel consolidation. In such operations, a mass of gunky material containing epoxy resin sometimes forms in the formation adjacent the well and in the bottom of the well, at times completely plugging the well. It is not known whether this gunky material is simply excess epoxy resin or epoxy resin in combination with deposit-forming materials from the formation. In any event, cleanout of this material to restore production of desired fluids can be an expensive operation.
Yet another problem encountered in most fluid-producing wells is corrosion of the downhole equipment. Such corrosion is caused by materials, such as sulfur compounds, present in the fluids being produced, which corrosion is aggravated by the presence of water which is usually present in varying amounts even in oil and gas producing formations. It has been found that such corrosion can also be prevented by coating the metallic well equipment with an epoxy resin. Again, a coating of the epoxy resin on the downhole equipment can be accomplished in generally the same fashion as the coating and consolidation of sand and gravel. It has also been found that following such treatments, wells can become plugged with a gunky material containing epoxy resin. Removal of this flow-restricting material is extremely expensive by conventional techniques.